JP2002068896A - Method and device for producing nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for obtaining a bulky nitride single crystal, in which it is possible to control the generation of a nucleus and by which the nitride single crystal having a high quality and a large size can be obtained at a relatively low temperature and low pressure. SOLUTION: A seed crystal is placed in a raw material for growing the nitride single crystal and then a crystal is grown by locally heating the seed crystal. Especially, it is preferable that crystal growth is carried out in such a manner that the seed crystal is locally heated while maintaining the temperature of the raw material for growing the nitride single crystal at a temperature at which the crystal hardly grows so that the temperature of the raw material present in the vicinity of the seed crystal is maintained at a high temperature at which the crystal can grow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for producing a nitride single crystal.

[0002]

2. Description of the Related Art In recent years, for example, gallium nitride based light emitting diodes and laser diodes have attracted attention as high luminance blue ultraviolet light emitting devices. Conventionally, these devices are manufactured by forming a gallium nitride crystal thin film by epitaxial growth on a sapphire substrate. Gallium nitride as such a thin film has a lattice constant difference (13.8%) between the substrate and the thin film, a thermal expansion coefficient difference (25.5%),
In addition, there is a problem in that it is difficult to obtain sufficient crystallinity because the difference between the wall surface and the opening is a bottleneck and the consistency with the substrate is poor.

In consideration of such problems, a method of manufacturing a device by homoepitaxial growth on a gallium nitride single crystal substrate has been studied, and it is important to realize a bulk gallium nitride single crystal serving as the substrate. It has become. However, bulk nitride single crystals such as gallium nitride (GaN) and aluminum nitride (AlN)
Since the equilibrium vapor pressure of nitrogen at the melting point is equal to or higher than 10,000 atm, the temperature of 1200 ° C., 8000 atm.
AlN requires higher temperature and pressure, and it is extremely difficult to grow such a bulk single crystal.

On the other hand, it has recently been found that a high quality bulk GaN single crystal can be synthesized at a relatively low temperature and low pressure of 800 ° C. and 100 atm by using a flux of Na, K or the like.

[0005]

The method of synthesizing a bulk GaN single crystal has attracted attention, but it has become clear that many problems still remain. This is because GaN single crystal growth is not practical unless the temperature and pressure exceed a certain value because nitrogen dissolves in the gallium melt by the action of an alkali metal such as Na and reacts to cause crystallization. No crystal growth is observed.
Therefore, it is considered that this is different from normal crystal growth in which a supersaturated state is brought about only by a temperature drop and crystal growth is performed.

That is, in the GaN single crystal growth in this method,
It is difficult to control natural nucleation conditions, and nucleation occurs in various places, resulting in a large amount of nuclei. Therefore, the synthesized GaN single crystal can be obtained only as a very small crystal. The present invention has been made based on the above-described crystal growth mechanism in order to solve such a problem, and the object thereof is to enable control of nucleation and to achieve high temperature at relatively low temperature and low pressure. It is an object of the present invention to provide a method and an apparatus for producing a high quality bulk nitride single crystal, for example, a GaN single crystal.

[0007]

In view of the above problems, the present invention employs the following means. That is, the method for producing a nitride single crystal according to the present invention is characterized in that a seed crystal is held in a nitride single crystal growth raw material, and the seed crystal is locally heated to grow the crystal. According to this means, the seed crystal is locally heated in the crystal growth raw material, and the crystal is grown only from the crystal raw material in the vicinity thereof. Therefore, the position of the crystal growth in the raw material and the crystal growth rate are reduced. Easy to control.

The nitride single crystal growth material is maintained at a low temperature at which almost no crystal grows, and the seed crystal is locally heated so that the growth material near the seed crystal can grow. It is preferable to carry out crystal growth while maintaining the temperature. According to this means, it is preferable that the crystal growth is performed smoothly without a sharp temperature difference between the crystal growth raw material and the seed crystal. In the present invention, “at a low temperature at which almost no crystal grows” refers to a low temperature at which no realistic crystal growth is observed in the crystal growth raw material, that is, a low temperature at which the crystal raw material is observed as if it has not reacted. It means that it is under temperature.

[0009] The crystal growth according to the present method has a chemically reactive element, whether the crystal growth is suddenly started from a certain temperature, or not noticed at the start because the crystal growth is progressing slowly at a very slow speed. Since it is unknown at this time, it was decided to express as described above. Further, it is preferable that a temperature near the seed crystal is measured, and a local heating temperature for the seed crystal is controlled to perform crystal growth. According to this means, since local temperature control of only the seed crystal is possible, the vicinity of the seed crystal can always be maintained at a temperature at which crystal growth is possible.

[0010] The nitride single crystal growing apparatus according to the present invention comprises: a raw material storage container for storing a nitride single crystal growth raw material;
A pressure vessel capable of accommodating the raw material storage container, and a heating device for heating the nitride single crystal growth raw material, wherein the pressure vessel is provided with a holding unit for holding the seed crystal in the growth raw material, The holder is provided with heating means for heating the seed crystal. According to this means, since the crystal growth raw material is heated by the heating device and the seed crystal is heated by the heating means, the seed crystal is at a high temperature at which the crystal can be grown, and the growth raw material is lower than the seed crystal. It can be maintained at a low temperature at which growth does not occur, and the above-described crystal growth method can be easily realized. In addition, since the crystal growth material is also heated to a certain temperature, a smooth crystal growth can be performed without a sudden temperature change between the entire growth material and a portion near the seed crystal in the growth material.

It is preferable that the holding portion is configured to be movable so that the position of the seed crystal in the pressure vessel can be changed. According to this means, the position of the seed crystal in the raw material can be changed according to the amount of the crystal growth raw material, and when the raw material is given a temperature distribution by heating by the heating device, A suitable seed crystal position can be controlled according to the temperature distribution. Further, the heating means comprises a heater capable of holding the seed crystal,
The heater is provided at a tip of a holding shaft extending from a moving device provided outside the pressure vessel, and drives the holding shaft by the moving device to change a position of the seed crystal in the pressure vessel. It is preferable that it is configured to be movable so that

According to this means, the seed crystal is held by the heater provided at the tip of the holding shaft extending from the moving device provided outside the pressure vessel, and the holding shaft is provided with the seed crystal in the pressure vessel. Since it is configured to be movable so that the position can be changed, the position of the seed crystal can be easily controlled only by moving the holding shaft. Further, it is preferable that a measuring unit for measuring the temperature of the growth raw material in the vicinity of the seed crystal and a control device for controlling the temperature of the heating means in accordance with the measured temperature are further provided.

According to this means, the temperature of the holding section for holding the seed crystal is measured by the measuring section, and the temperature of the heating means is controlled by the control device in accordance with the measured temperature. Maintained at a temperature favorable for crystal growth,
Crystal growth is promoted. Further, it is preferable that the raw material storage container is supported by a support having an elevating shaft for vertically moving the storage container. According to this means, the raw material storage container can be moved up and down with respect to the heating device by the elevating shaft to impart a temperature distribution to the crystal growth raw material. The crystal growth raw material around the crystal can be easily controlled to a temperature suitable for crystal growth.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method and an apparatus for producing a nitride single crystal of the present invention will be described in detail. The nitride single crystal to be obtained in the present invention is, as described above,
It grows in a process different from normal single crystal growth. That is,
When the condition exceeds the threshold value, there is a chemically reactive element in which crystal growth is started. Focusing on this difference in the growth mode, in the present invention, a nitride single crystal growth material (hereinafter, referred to as
The seed crystal is held in a crystal growth raw material), and the seed crystal is locally heated to grow the crystal. By local heating, crystal growth can be performed only at a certain position in the crystal growth material, and generation of natural nuclei at other positions in the material can be prevented.

More specifically, the entire crystal growth raw material is maintained at a low temperature at which almost no crystal grows, and the seed crystal is locally heated so that the vicinity of the seed crystal in the crystal growth raw material is locally formed. Crystal growth is performed while maintaining the temperature at a high temperature at which crystal growth is possible. Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a first embodiment of a nitride single crystal manufacturing apparatus according to the present invention. A nitride single crystal manufacturing apparatus (hereinafter simply referred to as a manufacturing apparatus) 1 includes a crystal growth raw material 2
A crucible 3 as a raw material storage container for storing the crucible 3, a pressure container 7 capable of storing the crucible 3, and a heating device 6 for heating the crystal growth raw material 2 stored in the crucible 3.

The crucible 3 is housed in an inner container 5 which is a closed container, and a heating device 6 is arranged around the inner container 5. These crucible 3, inner container 5, heating device 6
Are housed in the pressure vessel 7. Inner container 5
Is formed of carbon, ceramics, a high melting point metal and an alloy thereof, and the pressure vessel 7 is formed of high strength steel or the like. The inner container 5 is not necessarily provided, but it is preferable to provide the inner container 5 because the evaporation component from the crystal growth raw material may adhere to the heating device 6 and the operation of the heating device 6 may not be satisfactory.

The pressure vessel 7 is provided with a holding unit 10 for holding the seed crystal 4 in the growth raw material 2, and the holding unit 10 is provided with heating means for heating the seed crystal 4. The holding unit 10 is configured to be movable so that the position of the seed crystal 4 in the pressure vessel 7 can be changed. More specifically, the holding unit 10 includes a holding shaft 11 extending from a moving device 15 provided outside the pressure vessel 7 and a holding shaft 1.
And a heater 12 provided as a heating means provided at the end of the pressure vessel 7. The holding shaft 11 is driven by a moving device 15 so as to be movable so that the position of the seed crystal 4 in the pressure vessel 7 can be changed. It is configured. Seed crystal 4 is held by heater 12 and is heated to a certain temperature at which crystal growth is possible.

With such a holding shaft 11, the position of the seed crystal 4 in the crucible 3 can be easily adjusted, and the operation of taking out the grown crystal from the crucible 4 can also be easily performed. The holding shaft 1 for the pressure vessel 7 and the inner vessel 5
1 penetrates the sealing materials 18A and 18A, respectively.
B is provided so that the inside of the pressure vessel 7 and the inside of the inner vessel 5 can be kept airtight. A measuring unit (not shown) that measures the temperature of the crystal growth raw material 2 near the seed crystal 4 and a control device 16 that controls the temperature of the heater 12 according to the measured temperature are provided outside the pressure vessel 7. ing. Thereby, the seed crystal 4 and the crystal growth raw material 2 in the vicinity thereof can always be maintained at a temperature at which the crystal can be grown.

Next, a procedure for growing a crystal using the manufacturing apparatus will be specifically described. First, Ga and Na are stored in the crucible 3 as the crystal growth raw material 2. Ga is a direct raw material of the crystal, and Na is used as a flux. Next, the crucible 3 is set in the inner container 5 which is a closed container, and the inner container 5 is accommodated in the pressure container 7. Moving device 1
The holding shaft 11 extending from the pressure vessel 7 and the inner vessel 5
The seed crystal 4 is held by the heater 12 at the tip. With this configuration, the seed crystal 4 is used as the growth material 2
Held within.

The heater 12 and the control device 16 are connected by electric wires, and the inside of the pressure vessel 7 and the inside of the inner vessel 5 are maintained in a sealed state by the sealing members 18A and 18B. The inside of the pressure vessel 7 and the inside of the inner vessel 5 are exhausted by pipes 20A and 20B, respectively. Thereafter, nitrogen gas is supplied from nitrogen gas cylinders 22A and 22B through pipes 21A and 21B. At this time, the pressure in the pressure vessel and the pressure in the inner vessel are 50 to 100 atm. The crystal growth raw material 2 is heated by a heating device 6 and is maintained at 600 ° C., which is a low temperature at which crystals hardly grow. Such a low temperature region is considered to be in a range of about 150 ° C. to about 600 ° C.

The seed crystal 4 is heated to about 800 ° C. by the heater 12, and the temperature of the crystal growth raw material 2 near the seed crystal 4 is almost the same as that of the seed crystal 4. As a result, the crystal growth raw material is heated to a low temperature of 600 ° C., and the seed crystal is heated to a high temperature of 800 ° C., so that the temperature of the crystal growth raw material as a whole and the temperature near the seed crystal 4 where the crystal growth is performed become abrupt. No difference is made. That is, the crystal growth raw material is configured to be gradually heated to a high temperature near the seed crystal, and the crystal growth is performed smoothly. At this time, the heating device 6 may be divided into several heating zones up and down, and the temperature of each heating zone may be controlled to give a certain temperature distribution to the crystal growth raw material 2. According to this configuration, the temperature distribution can be given to the crystal growth raw material 2 in the crucible 4 without moving the crucible 4. As a result, the temperature of the crystal growth raw material 2 in the crucible 4, particularly the temperature of the crystal growth raw material 2 around the seed crystal 4, can be controlled to a temperature suitable for crystal growth.

At this time, the temperature is measured near the boundary between the crystal growth raw material 2 and the crucible 4, and the temperature of the heating device 6 is controlled so as not to reach a high temperature at which natural nucleation occurs. It is desirable to realize. By moving the holding shaft 11, the position of the seed crystal 4 in the crystal growth raw material 2 can be changed according to the amount of the raw material. In addition, by moving the holding shaft 10, an appropriate seed crystal position can be adjusted according to the temperature distribution due to the heating of the heating device 6. The crystal growth is performed while measuring the temperature in the vicinity of the seed crystal 4 by a measuring unit, controlling the temperature of the heater by a control device according to the measured temperature, and controlling the local heating temperature to the seed crystal.

Next, a second embodiment of the nitride single crystal manufacturing apparatus of the present invention will be described with reference to FIG. The manufacturing apparatus according to the present embodiment utilizes a normal vacuum-type vertical Bridgman furnace, and has a configuration in which a crucible as a raw material storage container can be moved up and down. The lower opening 5A of the inner container 5 is formed in a flange shape, and the inside of the inner container 5 is kept airtight by a plug 36 and a sealing material 37 which are detachable from the opening 5A. The plug 36 and the sealing material 37 are removed, and the crucible 3 is taken in and out. The inner container 5 is made of a material selected from the group consisting of carbon materials, ceramics, high melting point metals and alloys thereof.

The pressure vessel 7 is made of high-strength steel or the like, and the sealing member 37 is made of a heat-resistant polymer or a metal gasket. The entire inner container 5 and the heating device 6 arranged on the outer periphery of the inner container 5 are housed in a pressure container 7 as in the first embodiment. The pressure vessel 7 is a cylindrical body whose upper part is closed, and the lower opening 7A is closed by a plug 38 and a sealing material 39 which are detachable from the opening 7A, and the inside 7 of the pressure vessel is kept airtight. The plug 38 and the sealing material 39 are removed, and the crucible 3 and the inner container 5 are taken in and out.

Further, a support table 34 for supporting the crucible 3 is provided in the inner container 5, and the support table 34 is provided with an elevating shaft 35 for moving the crucible 3 up and down. The crucible 3 is this elevating shaft 3
The crystal growth raw material 2 in the crucible 3 can be given an appropriate temperature distribution by being vertically movable by an elevating device (not shown) through 5. The elevating shaft 35 also has a rotating function, and can rotate the crucible 3 to make the temperature distribution in the horizontal direction of the crystal growth raw material 2 uniform, thereby controlling the growth interface shape of the growing crystal.

Other structures such as piping for supply and exhaust and a holding shaft are the same as those of the first embodiment. Further, the holding portion 10 is formed in the same configuration as in the first embodiment, and the movable configuration in which the position of the seed crystal 4 in the pressure vessel 7 can be changed is also the same. Thereby, similarly to the first embodiment, the position of the seed crystal 4 in the crystal growth raw material 2 is
It can be changed according to the amount of the raw material. Further, the same applies in that the temperature of the heater is controlled by a measuring unit (not shown) and the control device 16.

Next, as an embodiment of the present invention, a process of manufacturing a single crystal using the manufacturing apparatus 31 will be described. As the crystal growth raw material 2, 20 g of Ga and 4 g of Na were put in the crucible 3 and set in the inner container 5. A heater 12 is provided at the tip of the holding shaft 11, and the seed crystal 4
2 is held. The holding shaft 11 is lowered, and the seed crystal 4
Is placed in the crystal growth raw material 2. The inside of the pressure vessel 7 and the inside of the inner vessel 5 are evacuated and evacuated by the pipes 20A and 20B, and then the inside of the pressure vessel 7 is provided by the pipe 21A.
In the inner container 5, N _{2 is} used as a nitrogen source through a pipe 21B.
Gas was introduced. The furnace body was heated to 600 ° C. at 50 ° C./hr and held for 60 minutes. The inside of the furnace was maintained at 50 atm.

The temperature of the seed crystal was raised to 800 ° C. by the heater 12, and the crystal was grown from the crystal growth raw material near the seed crystal while maintaining the temperature at 800 ° C. At this time, the crucible 3 may be lowered by the elevating shaft 35 to give a temperature distribution to the crucible, and the position of the crucible 3 may be adjusted so that crystal growth is further promoted. Further, the crucible 3 may be rotated by the elevating shaft 35 to promote the uniformization of the temperature of the crystal growth raw material 2 in the horizontal direction. In the crystal growth, the temperature in the vicinity of the seed crystal 4 is measured by a measuring unit, and the temperature of the heater 12 is controlled by the control device 16 according to the measured temperature to control the local heating temperature to the seed crystal 4. I went there.

After all the melt in the crucible 3 has crystallized,
The temperature was lowered to room temperature at 50 ° C / hr. The obtained crystal was a bulk single crystal having a sufficient size as a substrate for device fabrication by homoepitaxial growth. No nucleation was observed at any position other than the seed crystal. From the X-ray diffraction measurement results of the obtained GaN single crystal, GaN (00
A diffraction peak corresponding to the 02) plane was observed, and a rocking curve of this peak was measured to give a value of 70 seconds. Further, when a cathodoluminescence measurement was performed, band edge emission having a peak at 3.4 eV was observed. In addition, light emission from an energy level due to defects and impurities is not observed, and it is considered that the single crystal has few defects and impurities. From these results, it was found that the crystals were high quality bulk crystals.

Next, a comparative example of the present invention will be described.
20 g of Ga as a crystal growth raw material and 4 g of Na as a flux were stored in a crucible. The crucible was set in an apparatus as shown in FIG. 2 and evacuated, then nitrogen gas was introduced, and the temperature was raised to 800 ° C. at a rate of 50 ° C./hr.
The inside of the furnace was maintained at 50 atm. On the other hand, the seed crystal 4 was held by the heater 12 at the tip of the holding shaft 11 and was heated to 800 ° C. by the heater 12 to grow the crystal. as a result,
A large number of crystals having a size of about several microns were counted in the crucible, and the crystals grown in the seed crystal part were also polycrystals, and secondary nuclei were formed from the surface.

From the above results, it can be seen that if the entire crystal growth raw material is at a high temperature at which the crystal can be grown, crystal growth is performed at all parts of the crystal growth raw material, and many small nuclei are spontaneously generated. As a result, the amount of the raw material used for growing the seed crystal is reduced, and it is difficult to obtain a bulk crystal having a sufficient size. In addition, the growth rate of the crystal grown by this method is high at high temperatures, but it is very difficult to control the growth rate of a seed crystal in the raw materials when the entire crystal growth raw material is at high temperatures. It is.

Although the micro quality as a crystal is not considered to be significantly different from that of the above example and the comparative example, the crystal obtained in the example has a sufficient size and a beautiful shape. Was something. From these results, the growth of the seed crystal was maintained while maintaining the crystal growth raw material at a lower temperature than the seed crystal, where crystal growth was hardly observed, and maintaining only the seed crystal at a high temperature at which crystal growth was possible. It can be seen that the speed can be easily controlled and a high-quality bulk single crystal can be obtained.

Further, since the crystal growth raw material is maintained at a relatively low temperature, it is easy to set up a crystal growth observation window and the like.
It is also preferable in equipment management. As the flux, potassium and the like can be used. Further, as the nitrogen source, a nitride gas, a nitride-containing gas, or the like can be used in addition to the nitrogen gas described above. Further, the above-described method and apparatus for producing a single crystal are also suitable for producing another nitride single crystal such as AlN. The pressure at which the crystal is grown is preferably at least 50 atm, and the growth is performed while maintaining a constant value. The temperature at which the crystal can be grown is 700 ° C.
It is preferable that it is above.

In the above description, the holding shaft is provided so as to penetrate from the upper part of the pressure vessel, but may be provided so as to penetrate from the lower part of the pressure vessel. Further, the holding portion is not limited to the above-described structure, and any structure that can hold the seed crystal in the crystal growth material and can be heated can be employed.

[0035]

According to the present invention, the seed crystal held in the crystal growth raw material is locally heated to grow the crystal only from the crystal raw material in the vicinity of the seed crystal. The growth position and the crystal growth rate can be easily controlled, and a high quality and large bulk nitride single crystal can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of a nitride single crystal manufacturing apparatus according to the present invention.

FIG. 2 is a side sectional view showing a second embodiment of the nitride single crystal manufacturing apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nitride single crystal manufacturing apparatus 2 Nitride single crystal growth raw material 3 Crucible 4 Seed crystal 5 Inner vessel 6 Heating apparatus 7 Pressure vessel 10 Holding section 11 Holding axis 12 Heater 15 Elevating apparatus 16 Control apparatus 34 Supporting stand 35 Elevating axis

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 500244540 Masashi Yoshimura 2-10 Nobuhirocho, Fukuyama City, Hiroshima Prefecture (72) Inventor Kazuhiro Uehara 2-3-1 Shinhama, Araimachi Takasago City, Hyogo Prefecture Kobe Steel Takasago Co., Ltd. Inside the factory (72) Inventor Takatomo Sasaki 2-8 Yamada Nishi, Suita-shi, Osaka (72) Inventor Yusuke Mori 8-16-9, Private City, Katano-shi, Osaka (72) Inventor Masashi Yoshimura 2, Nobuhirocho, Fukuyama-shi, Hiroshima -10 F term (reference) 4G077 AA02 BE15 CF10 EA02 EA04 EG20 HA12

Claims (8)

[Claims] 1. A method for producing a nitride single crystal, comprising: holding a seed crystal in a nitride single crystal growth raw material; and locally heating the seed crystal to grow the crystal. 2. A nitride single crystal growth raw material is maintained at a low temperature at which almost no crystal grows, and the seed crystal is locally heated so that the growth raw material near the seed crystal can be grown. 2. The method for producing a nitride single crystal according to claim 1, wherein the crystal is grown while maintaining the temperature. 3. The nitride single crystal according to claim 1, wherein a temperature near the seed crystal is measured, and crystal growth is performed by controlling a local heating temperature of the seed crystal. Production method. 4. A raw material storage container for storing a nitride single crystal growth raw material, a pressure container capable of storing the raw material storage container,
A heating device for heating the nitride single crystal growth raw material, wherein the pressure vessel is provided with a holding unit for holding the seed crystal in the growth raw material, and the holding unit is a heating unit for heating the seed crystal. Means for producing a nitride single crystal. 5. The nitride single crystal production according to claim 4, wherein the holding unit is configured to be movable so that the position of the seed crystal in the pressure vessel can be changed. apparatus. 6. The heating means comprises a heater capable of holding the seed crystal, and the heater is provided at a tip of a holding shaft extending from a moving device provided outside the pressure vessel,
5. The apparatus according to claim 4, wherein the moving device drives the holding shaft to change the position of the seed crystal in the pressure vessel.
2. The nitride single crystal production apparatus according to 1. 7. The apparatus according to claim 1, further comprising: a measuring unit for measuring a temperature of the growth raw material in the vicinity of the seed crystal; and a control device for controlling a temperature of the heating unit in accordance with the measured temperature. Item 7. An apparatus for producing a nitride single crystal according to any one of Items 4 to 6. 8. The nitride monolith according to claim 4, wherein said raw material storage container is supported by a support having an elevating shaft for vertically moving said storage container. Crystal manufacturing equipment.